Overly bright = engaging to many, many people. Personally I find the bass to be the most engaging part of the music, which seems like common sense to me but oh well. Laid back is associated with dark sound, which again, to me seems like a misnomer.

I'm curious this myself. I have not heard the HD 650. But I have HD 600's, and I enjoy them enough. But I always feel that they are lacking something. I've considered trying the 650's, but I always hear people describe them as "boring".

Paired with the "right" amplifier, the HD-650 is everything BUT boring!

They are smooth and I can listen to them for hours and hours without tiring, but the music still feels alive. There's enough sparkle to the highs for me to engage with the music, but not too much that it gets annoying. Likewise, the bass and mid-range allow me to "get my groove on", without them feeling overpowering to me.

My pair are powered by a Graham Slee Solo, which I feel drive them really very well.

I think the fact that some users prefer a more upfront, aggressive sound signature, which is something the HD650 does not have. As a result, they attach the "boring" label to it. It all comes down to sound preference, as there are those that label Grados as murder on the ears because of their unique upfront sonic character.

I attribute this to the large soundstage which tends to be more comfortable to listen to than the treble attack from Grados. They're boring because they do everything well, and they've been out for a while, so people want to buy other things instead now. Other than that, they're still world class cans and among the best I've ever heard. The Sennheiser veil is exaggered as well. It's there, but only as a way to not fatigue your ears over time. The detail and timbre is all there and the bass is definitely real.

That being said, except for the HD800 which I have no experience with, no Senn will match the detail and attack of Grados. They're just too fast due tot he simple nature and the thin mylar membrane of the drivers. You get a lot of bass tradeoff from that unfortunately compared to Senns. Sennheiser needs to make amps though, it's unfortunate that they left that area blank and just have poor people guessing which amps to power these with. Although to be fair if you plug them into a Onkyo/Denon receiver, they do JUST fine.

What you think they're gonna claim that they make the best headphone in the world back in the day at 499 MSRP and not have it appeal to the masses? It's great at everything!

Because it is too laid back for energetic, aggressive music. Such is the stigma of all "all-rounders" which in reality only shine with slow, light music. They are relaxing cans but they will not engage you with fast music.